The present invention relates to a commutator with a short-circuit member assembly, a direct-current motor having the commutator, and a method for manufacturing the commutator.
Typically, in order to reduce a direct-current motor in size, it is desired that the size of a commutator provided in an armature of the motor be decreased. For example, Japanese Laid-Open Patent Publication No. 2005-137193 discloses a direct-current motor that decreases the axial dimension of a commutator by using a short-circuit member assembly configured by two groups of flat plate-like short-circuit pieces, which are stacked together in the axial direction of the commutator.
Each of the two groups of the short-circuit pieces of the aforementioned publication includes a plurality of short-circuit pieces that are arranged in the same plane. Each short-circuit piece includes an outer terminal, an inner terminal, and a connecting portion. The outer terminal is located radially outward. The inner terminal is arranged radially inward from the outer terminal and circumferentially offset from the outer terminal at a predetermined angle toward one side. The connecting portion connects the outer terminal to the inner terminal. A plurality of segments are circumferentially arranged around the outer circumference of the commutator. The number of the outer terminals of each the short-circuit piece group is equal to the number of the segments. The outer terminals of each short-circuit piece group are each electrically connected to the corresponding one of the segments. The two short-circuit piece groups are stacked together in such a manner that the connecting portions of one of the short-circuit piece groups extend across the connecting portions of the other the short-circuit piece group, as viewed axially. The outer terminals of one of the short-circuit piece groups contact the outer terminals of the other the short-circuit piece groups. The inner terminals of one of the short-circuit piece groups contact the inner terminals of the other the short-circuit piece group. The connecting portions of one of the short-circuit piece groups and the connecting portions of the other the short-circuit piece group are mutually spaced in the stacking direction of the two groups and thus held in mutual non-contact states. Insulating members formed of insulating resin material are each arranged between each circumferentially adjacent pair of the connecting portions of each short-circuit piece group. Each insulating member prevents short circuit between the corresponding circumferentially adjacent pair of the connecting portions.
To manufacture the short-circuit member assembly of the aforementioned document, the two short-circuit piece groups are placed in a mold while held in the stacked state. Then, the insulating resin material in a molten state is poured into the mold to shape the insulating members. However, since each connecting portion is elongated, the connecting portions are deformed by molding pressure acting on the connecting portions when the insulating members are shaped. Such deformation may cause short-circuit in the corresponding circumferentially adjacent pair of the connecting portions.